A large number of patients undergo joint replacement surgery each year. An estimated 540,000 patients in the U.S. undergo knee arthroplasty annually. Currently, implants made from metal, ceramic and/or ultra-high molecular weight polyethylene (UHMWPE) have been used in orthopedic joint arthroplasty or joint replacement. However, the use of such materials often necessitates high degree of bone and soft tissue sacrifice. For example, for hip replacement the femoral head is often entirely removed and replaced with a metal ball and stem implant. This results in the introduction of greater amounts of implant material into the patient's body which can corrode or may release ions or debris, such as metal ions or wear particles. The ions or particles may remain in the joint area or may travel through the blood to other parts of the body. The implant or the debris or ions it releases may cause bone resorption (osteolysis), inflammation, metal toxicity, pseudo-tumors, pain, and other problems.
As such, flexible polymer implants have been designed as medical implants for adhesion to bone and bone-like structures or surfaces. Some such implants have been designed to replace the current materials for joint replacement. For example, a compliant polymer material can be used as cartilage replacement, which provides a bone sparing alternative to implants made from traditional materials, e.g. ceramic, metal, polyethylene. Artificial cartilage implants can be formed with a lubricious bearing (articulating) surface for replacing cartilage and an attachment surface for fixation of the implant to bone for any joint in the body. In some cases, a hydrated polymer (e.g. hydrogel) material is used for forming the compliant polymer implant. Additionally, these flexible polymeric implants may contain a homopolymer, copolymer, or a fully interpenetrating polymer network (IPN's) and/or semi-interpenetrating polymer network (“semi-IPN's”). Polymer implants may also include accessible chemical functional groups such as amine, hydroxyl, carboxyl, or urethane groups, or combinations of functional groups that can be used to modify the characteristics of the implants. Examples of polymeric materials and implants containing these materials are more fully described in: U.S. application Ser. No. 12/499,041 filed Jul. 7, 2009; U.S. application Ser. No. 13/219,348 filed Aug. 26, 2011; U.S. application Ser. No. 13/347,647 filed Jan. 10, 2012; U.S. application Ser. No. 12/536,233 filed Aug. 5, 2009; Ser. No. 12/148,534 filed Apr. 17, 2008; U.S. application Ser. No. 13/418,294 filed Mar. 12, 2012; International Application No. PCT/US11/4936 filed Mar. 23, 2009; and International Application No. PCT/US12/20828 filed Jan. 10, 2012, which are all incorporated by reference in their entirety.
Another advantage of using polymeric material is the ability to create desirable mechanical properties in an implant. Implants can be created with high mechanical strength and wear-resistance while at the same time providing lubricity. This is particularly advantageous for joint implants where a polymer implant can be implanted on one side of a joint forming a polymer-on-cartilage articulation in the joint. The bone-facing side of the polymer implant can be designed to include a polymeric material providing strength and wear-resistance while the articulation side of the same implant has a hydrated polymer that provides lubricity. Additionally, a joint may include multiple implanted polymer devices where one device mates with another in articulation. Each polymer implant is affixed to respective bone surfaces in the joint and mate in a polymer-on-polymer articulation. The structure and polymeric composition of the implants ensure strength at the bone-facing sides and low friction at the articulation sides.
Although the versatility of polymeric materials has several advantages, one challenge is the difficulty in maintaining the shape and form of a compliant, flexible implant. Unlike metal counterparts, the shape of flexible polymeric materials can bend, distort, or change more easily due to the implant's environment. This is problematic where an unused implant changes shape during storage and is no longer viable for implantation when needed. Furthermore, shape changes during the implantation procedure are potentially dangerous where the form of the implant alters during or after the anchoring process. As such, there is a need for maintaining the desired shape or form of the implant prior to, during, and after delivery and implantation into a patient's body.
In addition to the above, another challenge with a flexible implant is the ability to properly position and affix the implant to a target location. Implants are commonly anchored to a bone or joint space by way of a curable adhesive or cement. Conventional adhesives or cements contain polymethylmethacrylate and involve the curing of the compound into a grout-like material where the adhesive interdigitates with features on the implant (such as grooves) to secure the implant to a surface. Other mechanisms of affixation also include chemical and/or physical adhesion, e.g., covalent bonds formed between reactive functional groups found on the device material or bone and the chemical groups in the adhesive polymer and/or a variety of non-covalent interactions such as absorption (e.g., chemisorption, physisorption), hydrophobic interaction, crystallite formation, hydrogen bonds, pi-bond stacking, van der Waals interactions and physical entanglements between the device and the cured adhesive copolymer (e.g., at the molecular level), mechanical interlocking. Physical adhesion may be the result of in-filling or interdigitating of a bump(s), a depression(s), a groove(s), a pore(s), a rough area(s), a space(s) and/or other surface features. Examples of adhesive compounds that can be used to anchor a flexible polymer implant include those described in: U.S. application Ser. No. 12/409,359 filed Mar. 23, 2009; U.S. application Ser. No. 13/542,464 filed Jul. 5, 2012; and U.S. application Ser. No. 13/573,788 filed Oct. 3, 2012, which are all incorporated by reference in their entirety.
Generally, such adhesive compounds are applied to a surface of the implant in an uncured form. Then when thermal, chemical, or light-curing is applied to the implant surface, the implant is affixed to the joint surface. A problem that arises with polymer implants is the need to adjust the position or shape of the implant during the curing process.
To address these challenges, embodiments described herein provide methods, devices, and systems that facilitate the delivery and attachment of a flexible implant to a bone or bone-like surface. Embodiments described allow an implant to be easily, quickly, and strongly attached to a bone surface with a desired implant shape. Some embodiments may deliver any implant to a bone joint surface, but may be especially useful for delivering and attaching a flexible polymer implant to a bone joint surface. In some examples, the devices and methods may allow an implant to conform to a shape, including an irregular shape, of a bone surface, thereby providing a better fit between the implant and the bone surface.
Embodiments described also provide for methods and devices that can be used to control the curing rate of the adhesive compound to allow repositioning or reshaping of the implant. For example, a user (e.g. physician) may be able to control the start of the attachment procedure such as curing (e.g. curing may be started only after the implant is properly placed in a joint) by using a delivery device with a curing rate feature. Once curing of an adhesive to hold an implant in place is started, then the process may proceed very quickly, reducing the possibility that an implant might move out of position before curing and implant attachment is completed. Moreover, embodiments described provide methods and devices that maintain or mold the shape of the implant during curing to ensure proper fixation. For example, shaping devices are provided to maintain, support, or conform the shape of the implant during adhesion to a joint surface.
Additionally, although embodiments may provide for flexible or compliant implants, the devices, methods, and systems described herein can also be used with an implant having a relatively stiff or rigid structure.